This invention relates to drainage apparatus and more particularly to a drainage device for draining fluids from a body cavity.
Drainage devices, such as thoracic drainage devices utilizing drainage bottles or chambers, are initially partially filled with a liquid such as water or a saline solution, to a level slightly above the bottom wall of the chamber. A tube or the like is used which extends through the upper wall and downwardly through the chamber with the lower end or outlet of the tube below the water level to provide the necessary underwater or liquid seal. A main disadvantage of this construction is that, as the level of drainage liquid rises above the lower end of the tube, the force necessary to expel liquid from the tube and fluid from the pleural cavity increases due to the increasing pressure head above the tube outlet thus making it increasingly difficult for the patient to expel fluid. In order to avoid this increasing liquid head, the tube may be adjusted by raising it as the liquid rises in the collection chamber. However, this requires continuous maintenance on the part of personnel.
In U.S. Pat. No. 3,545,440, a float member is connected to the bottom of a flexible drainage tube so that the lower end of the tube tends to maintain the liquid head substantially constant as the drainage liquid rises in the chamber. This latter arrangement, however, results in a relatively complicated and expensive structure. Another method of maintaining a constant head is to connect the chamber to a vacuum source instead of to atmosphere and manually vary the negative pressure applied as the liquid head increases. This latter method, of course, is also complicated and requires continuous monitoring.
In U.S. Pat. No. 2,936,757, a flexible bag having a pocket formed therein receives a drainage tube so that drainage flows into the liquid in the pocket which forms a liquid seal and then, as the pocket overflows, the liquid fills the main drainage collection chamber. This construction has certain disadvantages, for example, the bag is flexible and changes volume with changes in internal or external pressures. For example, when the pleural cavity off the patient has a negative pressure or if a suction force is applied to assist the drainage flow, the bag tends to collapse. Also, any tipping of the bag would tend to move the relatively small quantity of liquid out of the pocket which forms the liquid seal so that there is danger of breaking the liquid seal and allowing air to reach the interior of the drainage tube and pleural cavity. Also, where the liquid seal is of a relatively low volume, the occurrence of high negative pressures in the cavity, such as may occassionally occur during heavy gasping, may draw a sufficient amount of liquid into the drainage tube to cause the liquid seal to be broken.